1. Field of the Invention
The present invention relates to a computer system remote copying method and a computer system.
2. Description of the Related Art
To manage the large volume of data that grows day by day, computer systems used by corporations and the like include storage systems capable of storing large quantities of data. Storage systems for example create redundant storage areas based on a redundant array of independent disks (RAID) using hard disk drives or the like. These redundant logical storage areas are referred to as logical volumes, and provided to the host computers within the computer system.
In recent years computer systems have been constructed that have been strengthened against disasters such as earthquakes, fire, and the like. Computer systems with improved readiness against disasters have a main site and a back up site in a location separated from the main site. A host computer and a storage system are provided at both the main site and the back up site. The data that is managed at the main site is transmitted to the back up site as appropriate, and is also stored at the back up site.
The configuration in which a host computer and a storage system are each provided at a plurality of sites, and the data stored at each site is the same, as described above, is known as a disaster recovery configuration (Japanese Patent Application Laid-open No. 2005-250626, Japanese Patent No. 4124348). In a computer system having a disaster recovery configuration, it is possible to shorten the stoppage time of mission critical work when a disaster occurs at the main site which is normally used, by immediately switching to the back up site.
Methods for managing the duplication of data at the main site and at the back up site include synchronous remote copying and asynchronous remote copying, as disclosed in the above patent documents. In synchronous remote copying, when the host computer of the main site writes data to the storage system, the written data is sent to the storage system of the back up site. After the storage system of the main site has confirmed that the written data has been stored in the storage system of the back up site, it sends the host computer of the main site notification that processing the write command has been completed.
In contrast, in asynchronous remote copying, when the storage system at the main site has stored the write data from the host computer of the main site, it notifies the host computer that processing of the write command has been completed. Then, at appropriate timing, the write data is sent from the storage system of the main site to the storage system of the back up site. The storage system of the back up site stores the write data at a different timing than the timing at which the storage system of the main site received and stored the write data.
Synchronous remote copying and asynchronous remote copying differ as described above. Asynchronous remote copying is adopted when the communication distance between the main site and the back up site is long, or when a high response performance is required. In asynchronous remote copying, the host computer is notified of completion of processing without waiting for completion of storage of the write data at the back up site, so the write response time can be shortened.
Further, by carrying out remote copying between the storage system of the main site and the storage system of the back up site, the load on the host computer of the main site and the host computer of the back up site can be reduced.
In the case of a disaster recovery configuration using asynchronous remote copying, the host computer of the back up site cannot use the data (copy destination data) stored in the storage system of the back up site.
This is because asynchronous remote copying is carried out between storage systems without the intervention of the host computer, so the host computer of the back up site cannot confirm whether the current copy destination data is the latest data or not. Therefore, in the conventional art, the data stored in the storage system of the back up site cannot be used except for disaster recovery, so its availability is low.